Shaping of hollow workpieces

ABSTRACT

A hollow workpiece to be ironed is subjected to a relatively large frictional force at its interior engaged by a punch, and to a smaller frictional force at its outside engaged by a die, whereby tensile stresses in the ironed portion of the workpiece are decreased and larger reductions in wall thickness are rendered possible per die. Deep drawing may be combined with ironing and both performed during a single stroke of the punch.

Unlted States Patent 1151 3,685,337 Avitzur 51 Aug. 22, 1972 [54]SHAPING OF HOLLOW WORKPIECES 807,085 6/1951 Germany ..72/60 72 Inventor:Betzalel Avitzur, 17 N 31 St 834,626 5/1960 Great 131112111 ..72/82lemown, p 1 104 625,01 1 6/1949 Great Bntam .....72/349 [22] Filed: Dec.30, 1969 OTHER PUBLICATIONS [21] Appl. No.: 889,218 Promotion of FluidLubrication in Wire Drawing" by Christopherson et al.; pp. 643 653;Proc. Inst. 52 us. c1 ..72/347 Mech- Eng-i 1955- [51] Int. Cl. ..B2ld22/20 [58] Field of Search ..72/347, 348, 349, 370, 467, P Herbs 72/468,253; 29/12, 1.21, 1.3 AmmekEr'c Michelson [56] References Cited 1 1ABSTRACT UNITED STATES PATENTS A hollow workpiece to be ironed 1esubjected to a relat1vely large fr1ct1onal force at its mterlor engagedFuchs, Jr. a punch to a maller frictional force at out- 211,342 1/1879Palmer ..72/347 side engaged by a die whereby tensile Stresses i the3,360,157 12/1967 Bolt 61 a1. ..1 13/ 120 A ironed portion of theworkpiece are decreased and 1123,095 3/1949 K8116! ..72/349 largerreductions in wall thickness are rendered p Lyon ble p p drawing y becombined with iron LangCWlS 1 ing and perfonned during a Single Strokeof FOREIGN PATENTS OR APPLICATIONS P 1,468,073 12/ 1966 France ..72/60l8 CIaims, 26 Drawing Figures E l I 1 I I I 32 l R 1 7 i R. 1 ZONE 1-/PATENTEDwszz m2 3,685.33 7

sum 02 or 25 F/a. lb

i Y .IXVEXTOR. BETZALEL AV/TZU/P BY PATENTEDwszz I972 SHEET URUF 25 ZONEI lNvE N TOR. BETZALEL Al ITZUR PATENTEIJA um 3.335.337

I SHEET OSUF 25 ik LIMITED DUE TO WALL TENSION m .05 0' L O 3.0?

WEIGHTED IRONING FORCE SEMI-CONE ANGLE FIG. 30 WEIGHTED IRONING FORCE ASA FUNCTION BETZALEL AVITZUR IINVENTOR.

PATENTED M1922 I973 sum as or 25 SEMI-CONE ANGLE FIG. 3b WEIGHTEDIRONING FORCE AS A FUNCTION IBETZALEL AVITZUR INVENTOR.

OF (1 AND m $3 74 7 1 MY/M PATENTEDwczz 1912 sum 07 or 25 er LIMITED DUETO WALL TENSION WEIGHTED IRONING FORCE SEMI -CONE ANGLE FIG.40 WEIGHTEDIRONING FORCE AS A FUNCTION 7 OF 0 AND 1 A,.

BETZALBL' AVITZUR INVENTOR.

PATENTEDmszzmz 3.685337 sum near 2 1k LIMITED DUE TO WALL TENSION m, 0-,L 5

EQ.(9b

WEIGHTED IRONING FORCE SEMI-CONE ANGLE FIG. 4b WEIGHTED IRONING FORCE ASA FUNCTION OF 0 AND 1 A,.

BETZALEL' AVITZUR INVENTOR.

'1 lIIITIII SHEET OSUF 25 PATENTED M922 1972 womom @220: QwFIQEBSEMI-"CONE ANGLE FIG.5 WEIGHTED IRONING FORCE AS A FUNCTION OF a AND mBETZALBL RVITZUR INVENTOR.

I L KYLVLQ-V g PATENTEDAUG 22 I972 SEMI-CONE ANGLE FlG.6c| RELATIVE WALLTENSION AS A FUNCTION OF (2 AND m BBTZALEL .AVITZUB INVENTOR.

PATENTEflAuczz m2 SHEET llUF 25 SEMI-CONE ANGLE F|G.6b RELATIVE WALLTENSION AS A FUNCTION BETZALEL AVITZUR INVENTOR.

OF a AND m PATENTEDmcza m2 SHEET 120F 25 SEMI-CONE ANGLE FIG.70 RELATIVEWALL TENSION AS A FUNCTION OF 0 AND r /t BETZALEL AVITZUR INVENTOR.

PATENTED ms 22 I972 SHEET 13UF 25 SEMI -CONE ANGLE FlG.7b RELATIVE WALLTENSION AS A FUNCTION BETZALEL. AVITZUR OF 0 AND 1 /1,.

' INVENTOR.

SHEET l [1F 25 PATENTED M1822 I972 SEMI-CONE ANGLE FIG.8 RELATIVE WALLTENSION AS A FUNCTION OF a AND m BETZALEL AVITZU'R INVENTOR.

PATENTED M1522 I972 SHEET ISUF 25 MAXIMUM POSSIBLE THICKNESS RATIO SEMI-CONE ANGLE FIG.9 MAXIMUM POSSIBLE THICKNESS RATIO AS A FUNCTION OF 0 ANDm BETZALEL Avmzun INVENTOR.

I r I I L. 5 (MM.

PATENTED M1222 I972 SHEET 16 0F 25 SEMI-CONE ANGLE F|G.IO MAXIMUMPOSSIBLE THICKNESS RATIO AS A FUNCTION OF 0 AND m BETZALBL AvnzunINVENTOR.

PATENTEIIAUBZZIHTZ I 3.685337 SHEET 170T 25 POSSIBL'E THICKNESS RATIOIMPOSSIBLE THICKNESS RATIO b I I (I) IIHIIIW "rrvv-rrrrv-r r rrlrllrrriI I, I 'I'IIIIIIIIII/I SEMI-CONE ANGLE FIG.|I THICKNESS RATIO AS AFUNCTION OF a AND m I BBMALEL AVITZUR INVENTOR.

' POSSIBLE IMPOSSIBLE SHEET 180F 25 THICKNESS RATIO BETZALEL AVITZURINVENTOR.

gg/ f/ flm PATENTEDwszz I972 SEMI-CONE ANGLE AND rn F|G.l2 THICKNESSRATIG AS A FUNCTION OF a PATENTEnnuazz m2 SEMI-CONE ANGLE SHEET 19 0F 25WALL TENSION 0 s s 1 6 EQ.(l3c) EXISTS W ELIMINATED MANDREL FRICTIONFIG.I3 CRITICAL SEMI-CONE ANGLE OF THE DIE TO PREVENT WALL TENSION.

BET ZALEL AVITZUR INVENTOR.

1. In a method of shaping a hollow workpiece with the aid of a punch anda die having an aperture extending therethrough, said aperture includinga conical portion having a semi-cone angle Alpha ; the steps ofproviding said workpiece with a side wall having an inner and an outersurface; causing said punch to engage said inner surface of the sidewall of the hollow workpiece so that the latter is positioned on saidpunch; moving said punch with said workpiece thereon relative to saiddie and into said conical portion of the aperture thereof to iron saidside wall and thereby reduce the thickness and increase the lengththereof to a predetermined degree while subjecting said workpiece todifferential frictional forces including a predetermined, relativelylarge frictional force resulting from contact of said inner surface ofthe side wall with said punch, and a smaller frictional force acting onsaid outer surface of the side wall and resulting from movement of saidside wall relative to said die, said differential frictional forcesbeing effective to limit tensile stresses in the ironed portion of saidside wall during ironing; and controlling said differential frictionalforces in part by said semi-cone angle Alpha being in agreement with theequation wherein m1 constant friction factor at conical portion of thedie aperture, m2 constant friction factor at punch, to original wallthickness of side wall of workpiece, tf final wall thickness of sidewall of workpiece after ironing.
 2. A method as defined in claim 1,wherein said die has a single Ironing portion, and said workpiece isironed to a predetermined final degree during passage through saidsingle ironing portion.
 3. A method as defined in claim 1, including thestep of providing said punch with a surface rougher than the innersurface of said tapered aperture of the die, the relatively roughsurface of said punch being caused to engage said interior surface ofthe side wall of the workpiece.
 4. A method as defined in claim 1, inwhich said aperture of the die includes a substantially cylindricalportion, and the magnitude of said relatively large frictional force isin accordance with the expression L length of substantially cylindricalportion of die, sigma xb back pull stress in side wall of workpiece,sigma xf front pull stress in ironed portion of side wall, sigma o yieldstress of workpiece material.
 5. A method as defined in claim 4, whereinthe ironed portion of said side wall is kept substantially free oftensile stresses during the ironing step and, accordingly, saidexpression is reduced to
 6. A method as defined in claim 5, wherein saidsemi-cone angle Alpha of the conical portion of the die aperture issmaller than approximately 55* and thus the reduced expression isapproximately equal to
 7. A method as defined in claim 4, wherein theportion of said side wall emerging from said conical portion of the dieaperture is subjected to tensile stresses in accordance with theequation
 8. A method as defined in claim 4, in which the thickness ofsaid side wall is reduced in accordance with the equation wherein expexponential function of; and remaining symbols are as set forth in claim7.
 9. A method as defined in claim 8, in which the ironed portion ofsaid side wall is kept substantially free of tensile stresses during theironing step and, accordingly, the last-cited equation is reduced andmodified to wherein Alpha < or = Alpha cr ( Alpha cr critical value ofAlpha ).
 10. In a method of shaping a hollow workpiece with the aid of apunch and a die having an aperture extending therethrough, said apertureincluding a conical portion and a substantially cylindrical portion; thesteps of providing said workpiece with a side wall having an inner andan outer surface; causing said punch to engage said inner surface of theside wall of the hollow workpiece so that the latter is positioned onsaid punch; moving said punch with said workpiece thereon relative tosaid die and into said conical portion of the aperture thereof to ironsaid side wall and thereby reduce the thickness and increase the lengththereof to a predetermined degree while subjecting said workpiece todifferential frictional forces including a predetermined, relativelylarge frictional force resulting from contact of said inner surface ofthe side wall with said punch, and a smaller frictional force acting onsaid outer surface of the side wall and resulting from movement of saidside wall relative to said die, said differential frictional forcesbeing effective to limit tensile stresses in the ironed portion of saidside wall during ironing; and controlling said smaller frictional forceby providing hydrodynamic lubrication in the area in which said outersurface of the side wall of the workpiece passes through said apertureof the die, said hydrodynamic lubrication being obtained underconditions represented by the equation wherein Nu viscosity oflubricant, sigma o yield or flow stress of workpiece material, vf finalvelocity of workpiece material, to original thickness of side wall ofworkpiece, tf final thickness of side wall of workpiece after ironing,Alpha semi-cone angle of conical portion of aperture of die, L length ofsubstantially cylindrical portion of die, epsilon thickness of lubricantfilm at die exit, ( epsilon /tf)cr critical value of relative thicknessof lubricant film at die exit.
 11. A method as defined in claim 10, inwhich with friction at the die being negligible the portion of said sidewall emerging from said conical portion of the die aperture is subjectedto tensile stresses in accordance with the equation wherein sigma xffront pull stress in ironed portion of side wall, sigma xb back pullstress in side wall, m2 friction factor at punch; and remaining symbolsare as set forth in claim
 10. 12. In a method of shaping a cup-likeworkpiece from a substantially flat blank with the aid of a punch anddie means having an aperture extending therethrough, said apertureincluding a conical portion having a semi-cone angle Alpha ; the stepsof causing said blank to abut said die means; advancing said punchrelative to said die means so as to draw said blank into said apertureand impart thereto the form of a cup having a side wall and a bottomintegral therewith, said side wall having an outer and an inner surface;continuing the movement of said punch relative to said die means tointroduce said workpiece into said conical portion of the aperture ofthe die means and iron said side wall and thereby reduce the thicknessand increase the length thereof to a predetermined degree whilesubjecting said workpiece to differential frictional forces including apredetermined, relatively large frictional force resulting from contactof said inner surface of the side wall with said punch, and a smallerfrictional force acting on said outer surface of the side wall andresulting from movement of said side wall relative to said die means,said differential frictional forces being effective to minimizeapplication of forces to said bottom of the cup-shaped workpiece andthereby limit tensile stresses in the ironed portion of said side wallduring ironing; and controlling said differential frictional forces inpart by said semi-cone angle Alpha being in agreement with the equationwherein m1 constant friction factor at conical portion of the dieaperture, m2 constant friction factor at punch, to original wallthickness of side wall of workpiece, tf final wall thickness of sidewall of workpiece after ironing.
 13. A method as defined in claim 12,including the steps of starting said ironing substantially immediatelyafter formation of said bottom while keeping the ironed portion of saidworkpiece generally free of tensile stresses during ironing.
 14. Inapparatus for shaping a hollow workpiece provided with a side wallhaving an inner and an outer surface; die means having an apertureextending therethrough, said aperture including a conical ironingportion; a punch movable relative to said die means and arranged toengage said inner surface of the side wall of the workpiece foradvancing the latter into said ironing portion of the die aperture so asto iron said workpiece; first means for subjecting said workpiece to apredetermined, relatively large frictional force resulting from contactof said inner surface of the side wall with said punch; and second meansfor subjecting said workpiece to a smaller frictional force acting onsaid outer surface of the side wall and resulting from movement of saidside wall relative to said die means; said first and second means beingeffective to limit tensile stresses in said side wall during ironing;and said conical portion of the aperture of the die means having asemi-cone angle Alpha in accordance with the equation wherein Alphasemi-cone aNgle of ironing portion of die means, m1 constant frictionfactor at ironing portion of die means, m2 constant friction factor atpunch, to original thickness of side wall of workpiece, tf finalthickness of side wall of workpiece after ironing.
 15. Apparatus asdefined in claim 14, wherein said first means includes a punch surfacerougher than the surface of said aperture of the die means, said roughersurface of the punch being arranged to engage said inner surface of theside wall of the workpiece.
 16. Apparatus as defined in claim 15,wherein said second means includes an actuating device for moving saidpunch and workpiece relative to said die means at a rate sufficient forhydrodynamic lubrication of the area in which said outer surface of theside wall of the workpiece passes through said ironing portion of thedie aperture.
 17. Apparatus as defined in claim 14, wherein saidaperture of the die means includes a drawing portion preceding saidironing portion and cooperating with said punch for drawing saidworkpiece from a substantially flat blank to the shape of a cup and forthereby producing said side wall and a bottom integral therewith priorto and in series with the ironing operation; and wherein said drawingand ironing portions of the aperture of the die means are arranged soclose to each other that ironing will commence as soon as said bottom ofthe workpiece emerges from said drawing portion of the aperture of thedie means.
 18. Apparatus as defined in claim 17, wherein said drawingportion merges into said ironing portion.